Comparative Ellipsometric Analysis of Silicon Carbide Polytypes 4 H , 15 R , and 6 H Produced by a Modified Lely Method
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ative Ellipsometric Analysis of Silicon Carbide Polytypes 4H, 15R, and 6H Produced by a Modified Lely Method in the Same Growth Process D. D. Avrova, A. N. Gorlyaka, A. O. Lebedeva,b, V. V. Luchinina, A. V. Markova, A. V. Osipovc*, M. F. Panova, and S. A. Kukushkind a
St. Petersburg State Electrotechnical University “LETI,” St. Petersburg, 197376 Russia Ioffe Physical Technical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia c Mechanical Engineering Research Institute, Russian Academy of Sciences, St. Petersburg, 603024 Russia d St. Petersburg University of Information Technologies, Mechanics, and Optics (ITMO University), St. Petersburg, 197101 Russia *e-mail: [email protected] b
Received May 15, 2020; revised July 2, 2020; accepted July 2, 2020
Abstract—A model is suggested for a quantitative analysis of the dependence of the dielectric function of hexagonal silicon carbide polytypes on photon energy in the range of 0.7–6.5 eV. The model, which is the sum of two Tauc–Lorentz oscillators (main and minor) with a common energy gap, is used to describe three hexagonal silicon carbide polytypes (4H, 15R, 6H) obtained in the same growth process. Both C- and Si-faces of each polytype are analyzed. A number of conclusions are drawn about how the oscillator parameters depend on the degree of hexagonality of a polytype and on the type of a surface face. The strongest dependence is that the amplitude of the minor oscillator grows with increasing degree of hexagonality of a polytype. The increase in the energy gap on passing from the C-face (000 1 ) to the Si-face (0001) is also worthy of note. Keywords: silicon carbide, polytypes, dielectric function, ellipsometry. DOI: 10.1134/S1063785020100028
It is well known that a particular case of polymorphism, polytypism, is characteristic of materials with layered structure, such as silicon carbide (SiC) [1, 2]. In this case, different polytypes differ between one another only in the alternation order of atomic layers. Polytypes may significantly differ in some properties from each other, which is used for operation of various devices [2]. For example, the energy gap width of the cubic polytype 3C-SiC is 2.4 eV, and that of the hexagonal polytype 4H-SiC, 3.3 eV. Therefore diodes and HEMT transistors based on the 3C/4H heterojunction are believed to be quite promising [3]. The Raman spectra of various SiC polytypes are strongly different because the polytypes have different symmetries and, accordingly, various selection rules for optical transitions [4]. By contrast, the dependence of the dielectric function on the photon energy weakly depends on the symmetry and, accordingly, on the polytype. Nevertheless, certain patterns exist, but, to reveal these, it is necessary to use a model that will describe the dielectric function of SiC polytypes not only qualitatively, but also quantitatively. The goal of the present study was to examine the dependence of the dielectric function of SiC on the degree of hexagonality of a polytype
and on the face type (C o
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